From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 821B7C43381 for ; Fri, 8 Mar 2019 21:33:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 43FB520652 for ; Fri, 8 Mar 2019 21:33:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="aT1zb9Gp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726676AbfCHVd5 (ORCPT ); Fri, 8 Mar 2019 16:33:57 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:47648 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726388AbfCHVd5 (ORCPT ); Fri, 8 Mar 2019 16:33:57 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=f1uvKVxVhzDTR2+cHskxGsv/MTOUPRhC3M5x+AFK9hw=; b=aT1zb9GpuKazXic5RbeIbUInr Nm3KIW/aDZtYhhPcoHpW9/gc/UHckd9FVmPE4rqDRoHYmjQ6T8tHIJtsyXRyvYZJ7gJ96SaaIWJeZ WUZpDccJDJcZF8mqQEVTKQCI4s0ES8i0XP8aPdEYQ/CR2+YEfOPhPCucljqJKlYIR3h2V0RrkRVlC 23MA5j0/Dejqi4CK4qLREXFVbpzW8IabBCLzCub1qLoVDRxRFSLFFS3I9Ygj6nMqChARiDr5U1NJz 7H6ygUAObzSbl6UfVNGMFP/ARrsfuSZNODyuajdBpFrt4pYugvhjeuJ3dUGpkn5nZSkqZNcbkKrxn NwMvxlNXA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1h2N7h-00025K-7L; Fri, 08 Mar 2019 21:33:45 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 16F25981BBE; Fri, 8 Mar 2019 22:33:43 +0100 (CET) Date: Fri, 8 Mar 2019 22:33:43 +0100 From: Peter Zijlstra To: Josh Poimboeuf Cc: torvalds@linux-foundation.org, tglx@linutronix.de, hpa@zytor.com, julien.thierry@arm.com, will.deacon@arm.com, luto@amacapital.net, mingo@kernel.org, catalin.marinas@arm.com, james.morse@arm.com, valentin.schneider@arm.com, brgerst@gmail.com, luto@kernel.org, bp@alien8.de, dvlasenk@redhat.com, linux-kernel@vger.kernel.org, dvyukov@google.com, rostedt@goodmis.org Subject: Re: [PATCH 20/20] objtool: Add Direction Flag validation Message-ID: <20190308213343.GE2482@worktop.programming.kicks-ass.net> References: <20190307114511.870090179@infradead.org> <20190307115200.878625203@infradead.org> <20190308211603.fpjbd5avcuoox6xf@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190308211603.fpjbd5avcuoox6xf@treble> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 08, 2019 at 03:16:03PM -0600, Josh Poimboeuf wrote: > On Thu, Mar 07, 2019 at 12:45:31PM +0100, Peter Zijlstra wrote: > > Having DF escape is BAD(tm). > > > > Suggested-by: Linus Torvalds > > Signed-off-by: Peter Zijlstra (Intel) > > Can you elaborate on why (in the patch description)? Did this actually > find any occurrences? Nope, didn't find anything. Also, all DF users are in asm so I didn't really expect any. Having it escape would probably result in fairly instant wreckage though. DF=1 results in things like rep mov going _backwards_.